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Patent US3786356A successfully refreshed from Google Patents.
US3786356A
Expired / Lapsed
US
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Ground fault detector
Assignee: CHALLENGER ACQUISITION Corp
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Filing: 1972-06-30
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Granted: 1974-01-15
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Expires: 1992-06-30
Abstract
Abstract Ground fault protectors commonly use a differential current transformer for sensing ground-fault current, and a level detector causes opening of the load circuit in response to ground-fault current above a tripping level. A current loop develops around the core of the differential transformer in case a fault develops between the ''''white'''' or neutral load-circuit conductor and the ground-return current path, this loop having the effect of reducing the sensitivity of the ground-fault sensing means. A test signal is applied to the differential transformer at frequent short intervals, and tripping of a loadcircuit interrupter results if such reduced sensitivity should develop. The level detector is made less sensitive during application of the test signal, to prevent opening of the load circuit in response to the test signal, but even during the testsignal intervals the level detector remains responsive to greater-than-minimum ground-fault signals. The circuit interrupter opens in case of reduced sensitivity of the ground fault sensing means due to any cause.
Inventors
- 👤 C Macphee
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 14:12
CPC Classifications
H; H02; H02H; H02H3/00; H02H3/26; H02H3/32; H02H3/33; H02H3/331; H02H3/334; H02H3/335
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
303 words
A ground fault protector for a load circuit including a first conductor and at least one additional conductor connected to an alternating-current supply one terminal of which is connected to said first conductor and to ground, said protector including a circuit interrupter for opening the connection from the alternating current supply to the load circuit, first means for providing a trip signal to cause said circuit interrupter to open in response to the occurrence of a ground-fault current between said additional conductor and ground, said first trip-signal providing means including ground fault sensing means disposed between said load circuit and the grounded terminal of said alternating current supply connection, said first trip-signal providing means further including a first level detector for causing the circuit interrupter to open in response to output from the ground-fault sensing means of at least a prescribed magnitude, said ground fault protector including a second means for providing a trip-signal to cause the circuIt interrupter to open in case of a loss of sensitivity of said sensing means, said second trip-signal providing means including said sensing means and further including means for applying to said sensing means a test alternating current signal of prescribed magnitude and duration, said protector having means effective for the duration of the applied test signal for causing said first level detector to be non-responsive to that output of the sensing means which results from the applied test signal, and said second trip-signal providing means including a second level detector responsive to said sensing means for causing the circuit interrupter to open in case the output of the sensing means should be less than a prescribed level during application of the test signal, said second trip-signal providing means including means for coordinating the operation of said test signal applying means and said second level detector.
Claim 2
Dependent Claim
303 words
A ground fault protector for a load circuit including a first conductor and at least one additional conductor connected to an alternating-current supply one terminal of which is connected to said first conductor and to ground, said protector including a circuit interrupter for opening the connection from the alternating current supply to the load circuit, first means for providing a trip signal to cause said circuit interrupter to open in response to the occurrence of a ground-fault current between said additional conductor and ground, said first trip-signal providing means including ground fault sensing means disposed between said load circuit and the grounded terminal of said alternating current supply connection, said first trip-signal providing means further including a first level detector for causing the circuit interrupter to open in response to output from the ground-fault sensing means of at least a prescribed magnitude, said ground fault protector including a second means for providing a trip-signal to cause the circuIt interrupter to open in case of a loss of sensitivity of said sensing means, said second trip-signal providing means including said sensing means and further including means for applying to said sensing means a test alternating current signal of prescribed magnitude and duration, said protector having means effective for the duration of the applied test signal for causing said first level detector to be non-responsive to that output of the sensing means which results from the applied test signal, and said second trip-signal providing means including a second level detector responsive to said sensing means for causing the circuit interrupter to open in case the output of the sensing means should be less than a prescribed level during application of the test signal, said second trip-signal providing means including means for coordinating the operation of said test signal applying means and said second level detector.
Claim 3
Dependent Claim
92 words
A ground fault protector in accordance with claim 1, wherein said second trip-signal providing means includes means activated by said coordinating means for providing a trip signal to said second level detector to cause opening of the circuit interrupter, and wherein said second level detector is adapted to prevent the trip signal of said second trip-signal providing means from causing the circuit interrupter to open when the response of the sensing means to the applied test signal evidences proper performance of the test signal applying means and the ground fault sensing means.
Claim 4
Dependent Claim
58 words
A ground fault protector in accordance with claim 1, wherein said coordinating means includes means coordinated with the application of the test signal to the sensing means for reducing the sensitivity of said first level detector so as to be non-responsive to that level of output of said sensing means which results when a test signal is applied.
Claim 5
Dependent Claim
41 words
A ground fault protector in accordance with claim 1, wherein said level of level detector has a time delay characteristic rendering it non-responsive to the output of the sensing means in response to the level and duration of the applied signal.
Claim 6
Dependent Claim
39 words
A ground fault protector in accordance with claim 1, including means causing said test signal applying means to produce test signals automatically at frequent intervals, the duration of each test signal being a small fraction of each such interval.
Claim 7
Dependent Claim
116 words
A ground fault protector for a load circuit, including means for interrupting the load circuit, ground-fault sensing means, first means responsive to output from said ground-fault sensing means of at least a threshold level for causing said interrupting means to break the load circuit, and means for testing said ground-fault sensing means to verify the effectiveness thereof, said last-named means including means operative during test periods for applying a test signal to said sensing means, and second means responsive to said sensing means and coordinated with said test signal applying means for causing the interrupting means to break the load circuit in case of sub-normal output of the sensing means in response to the test signal.
Claim 8
Dependent Claim
116 words
A ground fault protector for a load circuit, including means for interrupting the load circuit, ground-fault sensing means, first means responsive to output from said ground-fault sensing means of at least a threshold level for causing said interrupting means to break the load circuit, and means for testing said ground-fault sensing means to verify the effectiveness thereof, said last-named means including means operative during test periods for applying a test signal to said sensing means, and second means responsive to said sensing means and coordinated with said test signal applying means for causing the interrupting means to break the load circuit in case of sub-normal output of the sensing means in response to the test signal.
Claim 9
Dependent Claim
49 words
A ground fault protector in accordance with claim 1, further including means effective during application of the test signal for rendering said first responsive means ineffective to cause operation of said interrupting means in response to output of said sensing means resulting from application of said test signal thereto.
Claim 10
Dependent Claim
78 words
A ground fault protector in accordance with claim 1, further including means effective during application of the test signal for rendering said first responsive means ineffective to cause operation of said interrupting means in response to output of said sensing means resulting from application of said test signal thereto, without interfering with operation of the interrupting means in response to output of the sensing means substantially greater than the output resulting from application of the test signal thereto.
References Cited (Backward Citations)
US3638072A
Cited
US3555360A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-01-14 | 1977-07-16 | 1978-01-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-01-14 | 1981-07-16 | 1982-01-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-01-14 | 1985-07-16 | 1986-01-15 | $7700.00 | Window Closed / Lapsed |